This invention relates to polymers and their latexes, solutions, dispersions and blends used to produce gloves and other articles having superior electrostatic dissipative properties.
Polymeric materials for use in electrostatic discharge (xe2x80x9cESDxe2x80x9d, xe2x80x9cstatic dissipativexe2x80x9d or xe2x80x9cantistaticxe2x80x9d) applications fall into two categories: rubbery or thermoplastic. Typically rubbery and thermoplastic materials are used in different applications and are made by different manufacturing methods. The ESD properties are achieved by incorporating hydrophilic moieties, such as various ethoxylates, or electroconductive fillers such as carbon black, metals, or salts. Many of these systems have shortcomings. Additives by their very nature can have widely variable results due to non-uniform dispersion in the matrix. They also can lose effectiveness if they extract from the matrix and/or deteriorate over time.
Achieving ESD properties in articles that are designed to be flexible rather than rigid provides further challenges. Some of the traditional ingredients in the prior art such as carbon black, metal powders and wires, electroconductive polymers, and inorganic fillers, can stiffen an article. This is not important in plastic applications, but will present a significant issue for articles that must be flexible.
In addition, ingredients in a flexible matrix, by their very nature, are more mobile than in a plastic matrix. Flexible articles such as gloves and papers are designed to bend, flex, and stretch under contact with moist skin. These conditions are more conducive to creating motion at the molecular level, which could increase the likelihood for water-soluble materials and fillers to bloom, transfer or flake off the surface. Any particulate matter coming off articles can potentially cause damage in a critical environment where antistatic properties are desired, such as xe2x80x9cclean roomxe2x80x9d applications and electronics manufacturing.
Traditional materials for making ESD clean room articles incorporate conductive fillers, fibers, ionic materials, carbon black, or application of a surface coating. Shortcomings of these articles include extraction or deterioration over time, non-homogeneity, and a need for humidity to dissipate static charges effectively. Many articles such as gloves used in a clean room are manufactured under special conditions to minimize particulate contamination. For example, additional post-leach or water-soak processes in glove manufacturing will remove particulate contamination.
Current gloves used in clean room environments typically are made from latexes (also known as emulsions or latex emulsions) or dispersions of natural rubbers, acrylonitrile-butadiene rubbers, styrene-butadiene rubbers, polyvinylchlorides, polychlorobutadienes, and polyurethanes. Latexes typically are prepared by polymerization of monomers in a water medium, while dispersions are prepared by distribution of polymers in a water medium following polymerization. Gloves made from these polymers under current standard conditions of compounding and processing typically have a surface resistivity of 1xc3x971011 to 1xc3x971013 ohms/square and a static decay time greater than 1 second. Specialty gloves are currently on the market which offer antistatic or conductive features, incorporate additives such as carbon black during compounding, and have published surface resistivity values as low as 1xc3x97104 ohms/square.
The most accepted method of glove manufacturing is the coagulant dipping process, followed by subsequent leaching and curing cycles. In this process, a preheated and cleaned glove mold (also called a xe2x80x9cformerxe2x80x9d) is dipped into a calcium nitrate salt solution, and dried to tackiness. This salt-coated mold is dipped into a compounded latex or polymer dispersion, causing the latex or polymer dispersion to coagulate on the mold and form a glove. The glove is then leached in water to remove the salt, dried and cured to achieve final properties. Thus, an essential property of the latex or polymer dispersion is its ability to coagulate, forming an article.
The most widely used approach to render polymers antistatic is incorporating a polyethyleneglycol (PEG) moiety into the backbone of the polymer. PEG is a hydrophilic material and attracts moisture into the article, thus reducing its resistivity. Since it is polymerized into the backbone of the polymer, it is not extractable. For example, U.S. Pat. No. 4,543,390 relates to graft copolymers prepared by emulsion polymerization of certain polyethyleneglycol monomers and optionally certain vinyl monomers in the presence of rubbers. The graft copolymers subsequently are blended with compatible thermoplastic resins. However, the polyethyleneglycol monomers which render polymers antistatic also yield polyvalent ion-stable polymer emulsions which are unsuitable for glove making by coagulant dipping processes. See R. H. Ottewill et al, Colloid and Polymer Science, Vol. 266, No. 6, p. 547 (1988), and R. H. Ottewill, Emulsion Polymerization and Emulsion Polymers (Editors: P. A. Lovell and M. S. El-Aaser), J. Wiley and Sons (1997). p. 104 (1997).
U.S. Pat. No. 4,302,558 and U.S. Pat. No. 4,384,078 relate to antistatic graft copolymers obtained by graft-polymerizing a vinyl or vinylidene monomer onto a rubber trunk polymer which comprises a polyalkylene oxide monomer comprising 4 to 500 alkylene oxide groups together with an ethylenic unsaturation, and a conjugated diene and/or an alkyl acrylate. However, as shown in the examples below, the graft copolymers are unsuitable for glove making by coagulant dipping processes.
Unexpectedly, this invention demonstrates that blends of certain PEG-containing latexes, solutions or dispersions with typical glove-making latexes or dispersions are suitable for making gloves and other articles by coagulant dipping processes. Also unexpectedly, certain PEG-containing latexes, solutions or dispersions are suitable for making gloves and other articles by coagulant dipping processes even in the absence of said typical glove-making latexes or dispersions. Further, articles made from the compositions of this invention are inherently static dissipative and will not bloom, rub-off or extract during use. In particular, articles such as gloves made from the compositions of this invention, and that meet ASTM examination standards for target tensile and elongation properties, will also have a surface resistivity value below 1xc3x971011 ohms/square per square, a static decay time of less than 1 second, or both.
The materials of the present invention suitable for making antistatic articles by coagulant dipping processes are blends of (A) one or more step (1) polymers (in latex, solution or dispersion form) of (a) at least one reactive macromer of at least one alkylene oxide having at least one functional group capable of free-radical transformation, (b) optionally, one or more ethylenically unsaturated monomers having at least one carboxylic acid group, and (c) optionally, one or more free radically polymerizable comonomers, and (B) one or more step (2) other polymer latexes or dispersions of such polymers as natural rubber, conjugated-diene-containing polymers, hydrogenated styrene-butadiene triblock copolymers, chlorosulfonated polyethylenes, ethylene copolymers, acrylic and/or methacrylic ester copolymers, vinyl chloride copolymers, vinylidene copolymers, polyisobutylenes, polyurethanes, polyureas, and poly(urethane-urea)s. The term xe2x80x9cfree-radical transformationxe2x80x9d means being capable of reacting by a free-radical mechanism, examples including free-radically polymerizable monomers, chain transfer agents, or chain terminating agents.
Also suitable for making antistatic articles by coagulant dipping processes, even in the absence of said step (2) other polymer latexes or dispersions, are step (1) polymers (in latex, solution or dispersion form) of (a) at least one reactive macromer of at least one alkylene oxide having at least one functional group capable of free-radical transformation, wherein said macromer comprises less than about 10 wt. % of total polymer weight in the step (1) latex, solution or dispersion (b) optionally, one or more ethylenically unsaturated monomers having at least one carboxylic acid group, and (c) one or more free radically polymerizable comonomers.
The blends of the present invention comprise (A) one or more step (1) polymers (in latex, solution or dispersion form) of (a) at least one reactive macromer of at least one alkylene oxide having at least one functional group capable of free-radical transformation, (b) optionally, one or more ethylenically unsaturated monomers having at least one carboxylic acid group, and (c) optionally, one or more free radically polymerizable comonomers, and (B) and one or more step (2) other polymer latexes or dispersions.
In step (1) the (a) at least one reactive macromer of at least one alkylene oxide having at least one functional group capable of free-radical transformation is reacted to form latexes, solutions or dispersions with (b) optionally, one or more ethylenically unsaturated monomers having at least one carboxylic acid group, and (c) optionally, one or more radically polymerizable monomers, such as acrylic esters, methacrylic esters, conjugated dienes, styrenic monomers, vinyl esters, vinyl ethers, conjugated dienes, unsaturated nitrites and other polar monomers.
The following definitions apply throughout this specification. All weight percentages of polymers, latexes, and other materials are expressed on a dry weight basis. The term xe2x80x9cpolymerxe2x80x9d refers to homopolymers as well as copolymers. The term xe2x80x9cstep (1) polymerxe2x80x9d or xe2x80x9cpolymer (1)xe2x80x9d means a latex-forming, solution-forming or dispersion-forming polymer that is the primary component of a respective step (1) latex, solution or dispersion. Similarly, the terms xe2x80x9cstep (2) polymerxe2x80x9d or xe2x80x9cpolymer (2)xe2x80x9d means a latex-forming or dispersion-forming polymer that is the primary component of a respective step (2) other polymer latex or dispersion. The term xe2x80x9cstep (1) compositionxe2x80x9dmeans a step (1) latex, solution or dispersion. Similarly, the term xe2x80x9cstep (2) compositionxe2x80x9d means a step (2) other polymer latex or dispersion. The term xe2x80x9cother polymer latex or dispersionxe2x80x9d means a latex or dispersion other than a step (1) polymer latex or dispersion. The term xe2x80x9cpolymerized unitsxe2x80x9d means polymerized monomeric molecules, e.g., polybutadiene can be said to comprise polymerized units or molecules of butadiene monomer.
Polymerized reactive macromer (a) typically may comprise from about 0.1 wt. % to 100 wt. %, preferably from about 1 wt. % to about 30 wt. %, of the step (1) polymer. Polymerized monomer (b) typically may comprise from 0 wt. % to about 10 wt. %, preferably from about 3 wt. % to about 7 wt. %, of the step (1) polymer. Polymerized monomer (c) typically may comprise from 0 wt. % to about 99 wt. %, preferably from about 1 wt. % to about 70 wt. %, of the step (1) polymer.
One or more one step (1) compositions are then blended with one or more step (2) compositions incorporating polymers such as those of natural rubber, conjugated-diene-containing polymers, hydrogenated styrene-butadiene triblock copolymers, chlorosulfonated polyethylenes, ethylene copolymers, acrylic and/or methacrylic ester copolymers, vinyl chloride copolymers, vinylidene copolymers, polyisobutylenes, polyurethanes, polyureas, and poly(urethane-urea)s. The step (2) compositions typically may comprise from about 2 wt. % to about 99.5 wt. %, and preferably from about 50 wt. % to about 99 wt. %, of the blend of step (1) compositions and step (2) compositions.
Reactive macromers of alkylene oxides having at least one functional group capable of free-radical transformation are well known in the prior art. Such macromers have the formula (I):
Xxe2x80x94(Yxe2x80x94O)nxe2x80x94Zxe2x80x83xe2x80x83(I)
wherein Y is a straight or branched chain alkylene radical having 1 to 6 carbon atoms, preferably 2 to 4 carbon atoms, X is a functional group capable of free-radical transformation, such as acrylate, which may be represented by the formula H2Cxe2x95x90CHC(O)Oxe2x80x94, methacrylate, which may be represented by the formula H2Cxe2x95x90C(CH3)C(O)Oxe2x80x94, allyl ether, which may be represented by the formula H2Cxe2x95x90CHCH2Oxe2x80x94, vinyl ether, which may be represented by the formula H2Cxe2x95x90CHOxe2x80x94, vinylbenzyl, vinylsulfonic ester, which may be represented by the formula H2Cxe2x95x90CHSO3xe2x80x94, or mercaptan, Z is H, CmH2m+1, phosphate, or the same as X, and m is 1 to 8, preferably 1 to 3. xe2x80x9cnxe2x80x9d may vary to achieve the desired molecular weight (average) set forth below. Z is preferably H or methyl. X is preferably acrylate or methacrylate. Examples of suitable reactive monomers include methoxy polyethylene oxide (meth)acrylate (also known as methoxypolyethylene glycol methacrylate or xe2x80x9cMePEGMAxe2x80x9d), methoxy polyethylene oxide allyl ether, polyethylene oxide allyl ether, butoxy polyethylene oxide (meth)acrylate, p-vinylbenzyl terminated polyethylene oxide, polyethylene oxide di(meth)acrylate, polyethylene oxide thiol, polyethylene oxide maleimide, polyethylene oxide vinylsulfone, and the like. Mixtures of the reactive macromers may also be used. Preferred reactive macromers include methoxy polyethylene oxide (meth)acrylate, methoxy polyethylene oxide allyl ether, and polyethylene oxide allyl ether. Suitable reactive macromers may have molecular weights (average) from about 100 to about 10,000, preferably from about 100 to about 5,000, and more preferably from about 300 to about 2,000.
Unexpectedly, it was discovered that the step (1) compositions can be used without the step (2) compositions in making articles such as gloves by the coagulant dipping process described hereafter, provided that the amount of polymerized units of at least one reactive macromer of at least one alkylene oxide having at least one functional group capable of free-radical transformation is present but comprises less than about 10 wt. %, preferably less than about 8 wt. %, and more preferably less than about 6 wt. % of total polymer weight in the step (1) composition.
The step (1) compositions preferably include polymerized units of at least one ethylenically unsaturated monomer having at least one carboxylic acid group, and preferably one or two carboxylic acid groups. Examples of such monomers include acrylic acid, methacrylic acid, itaconic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, vinylacetic acid, mesaconic acid, citraconic acid, 2-acrylamido-2-methylpropanesulfonic acid, alkali metal salts of the above acids and amine or ammonium salts thereof. Acrylic acid and methacrylic acid are preferred. The polymerized ethylenically unsaturated monomers having at least one carboxylic acid group typically may comprise from 0 wt. % to about 10 wt. %, preferably from about 3 wt. % to about 7 wt. %, of polymer (1). Presence of the polymerized ethylenically unsaturated monomer having at least one carboxylic acid group as part of polymer (1) is desirable for the coagulant dipping processes described hereafter, but not for other glove making processes known to those skilled in the art.
Optionally one or more free radically (or xe2x80x9cradicallyxe2x80x9d) polymerizable comonomers may be useful in preparing polymer (1) of the step (1) compositions. Examples of such radically polymerizable comonomers include acrylic esters, methacrylic esters, unsaturated nitrites, styrenic monomers, vinyl esters, vinyl ethers, conjugated dienes, other monomers, and mixtures thereof.
Acrylic esters and methacrylic acid esters useful in preparing the step (1) compositions include those having the formula II: 
wherein R1 is hydrogen or a methyl group, and R2 contains 1 to 12 carbon atoms and optionally also one or more sulfur, nitrogen, halogen or oxygen atoms. Preferably R2 is an ethyl or butyl group. Examples of suitable acrylate esters include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, and n-decyl acrylate. Examples of suitable methacrylate esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, n-amyl (meth)acrylate, n-hexyl (meth)acrylate, isoamyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate, 2-sulfoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, glycidyl (meth)acrylate, benzyl (meth)acrylate, allyl (meth)acrylate, 2-n-butoxyethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, sec-butyl-(meth)acrylate, tert-butyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, cinnamyl (meth)acrylate, crotyl (meth)acrylate, cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, furfuryl (meth)acrylate, hexofluoroisopropyl (meth)acrylate, methallyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, 2-methoxybutyl (meth)acrylate, 2-nitro-2-methylpropyl (meth )acrylate, n-octyl (meth )acrylate, 2-ethylhexyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 2-phenylethyl (meth)acrylate, phenyl (meth)acrylate, propargyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, norbornyl (meth)acrylate, acrylamide and its derivatives, and tetrahydropyranyl (meth)acrylate. Mixtures of acrylic and methacrylic acid esters may be used. The polymerized acrylic and methacrylic acid esters typically may comprise from 0 wt. % to about 50 wt. %, from 0 wt. % to about 20 wt. %, and more preferably from 0 wt. % to about 10 wt. %, of polymer (1).
Suitable unsaturated nitrile monomers useful in preparing the step (1) compositions include acrylonitrile or an alkyl derivative thereof, the alkyl preferably having from 1 to 4 carbon atoms, such as acrylonitrile, methacrylonitrile, and the like. Also suitable are unsaturated monomers containing a cyano group such as those having the formula III:
CH2xe2x95x90C(R)CO(O)CH2CH2CNxe2x80x83xe2x80x83(III)
wherein R is H or CnH2n+1 and n is 1 to 4 carbon atoms. Other examples of unsaturated nitrile monomers include CH2xe2x95x90C(CN)2, CH3xe2x80x94CHxe2x95x90CHxe2x80x94CN, NCxe2x80x94CHxe2x95x90CHxe2x80x94CN, 4-pentenenitrile, 3-methyl-4-pentenenitrile, 5-hexenenitrile, 4-vinyl-benzonitrile, 4-allyl-benzonitrile, 4-vinyl-cyclohexanecarbonitrile, 4-cyanocyclohexene, and the like. Mixtures of the unsaturated nitriles may also be used. Acrylonitrile and methacrylonitrile are preferred. The polymerized unsaturated nitrile monomers typically may comprise from 0 wt. % to about 60 wt. %, preferably from about 5 wt. % to about 45 wt. %, of polymer (1).
The xe2x80x9cstyrenic monomersxe2x80x9d useful in preparing the step (1) compositions may be defined as monomers containing a carbon-carbon double bond in alpha-position to an aromatic ring. The styrenic monomers may be represented by the following formulae: 
wherein n is an integer from 0 to 2; R1, R2, R3, R4, R5, R6, and R7 are selected from the group consisting of H, CH3, CmH2m+1, OH, OCH3, OCmH2m+1, COOH, COOCH3, COOCmH2m+1, Cl and Br, m is an integer from 2 to 9, and R8 is selected from the group consisting of H, CH3, CmH2m+1, and C6H5.
Examples of suitable styrenic monomers useful in preparing step (1) compositions include styrene, alpha-methylstyrene, tertiary butylstyrene, ortho-, meta-, and para-methylstyrene, ortho-, meta- and para-ethylstyrene, o-methyl-p-isopropylstyrene, p-chlorostyrene, p-bromostyrene, o,p-dichlorostyrene, o,p-dibromostyrene, ortho-, meta- and para-methoxystyrene, indene and its derivatives, vinyinaphthalene, diverse vinyl (alkyl-naphthalenes) and vinyl (halonaphthalenes) and mixtures thereof, acenaphthylene, diphenylethylene, and vinyl anthracene. Mixtures of styrenic monomers also may be used. Styrene is preferred. The polymerized styrenic monomers typically may comprise from 0 wt. % to about 65 wt. %, preferably from about 5 wt. % to about 40 wt. %, of polymer (1).
Vinyl ester monomers derived from carboxylic acids containing 1 to 14 carbon atoms also may be useful in preparing the step (1) compositions. Examples of such vinyl ester monomers include vinyl acetate, vinyl propionate, vinyl hexanoate, vinyl 2-ethylhexanoate, vinyl octanoate, vinyl pelargonate, vinyl caproate, neo esters of vinyl alcohol, vinyl laurate, and the like, as well as mixtures thereof. The polymerized vinyl ester monomers typically may comprise from 0 wt. % to about 99.5 wt. %, preferably from 0 wt. % to about 30 wt. %, of polymer (1).
Vinyl ethers may be useful in preparing the step (1) compositions. Examples of vinyl ethers include methyl-, ethyl-, butyl, iso-butyl vinyl ethers and the like. The polymerized vinyl ether monomers typically may comprise from 0 wt. % to about 50 wt. %, preferably from 0 wt. % to about 30 wt. %, of polymer (1).
Conjugated diene monomers containing 4 to 10 carbon atoms, and preferably from 4 to 6 carbon atoms, also may be useful in preparing the step (1) compositions. Examples of such conjugated diene monomers include butadiene, isoprene, cis-1,3-pentadiene, trans-1,3-pentadiene, cis-1,3-hexadiene, trans-1,3-hexadiene, 2-ethylbutadiene, 2-n-propylbutadiene, 2-i-propyl butadiene, 2-t-butylbutadiene, 2-amylbutadiene, 2-n-octylbutadiene, 4-methylpentadiene, cis-3-methylpentadiene, trans-3-methylpentadiene, cis-2-methylpentadiene, trans-2-methylpentadiene, 2,3-dimethylbutadiene, cis,cis-2, 4-hexadiene, cis,trans-2,4-hexadiene, trans,trans-2,4-hexadiene, 2-methyl-3-ethylbutadiene, 2-methyl-3-i-propylbutadiene, 2-methyl-3-n-butylbutadiene, myrcene, cis-1-phenylbutadiene, trans-1-phenylbutadiene, 2-phenyl butadiene, 1,3-cyclopentadiene, 1,3-cyclohexadiene, 2-fluorobutadiene, 1-chlorobutadiene, 2-chlorobutadiene, 2,3-dichlorobutadiene, 2-bromobutadiene, sorbic acid, cis-1-cyanobutadiene, 2-methoxybutadiene and like, as well as mixtures thereof. Butadiene is more preferred. The polymerized conjugated diene monomers typically may comprise from 0 wt. % to about 99.5 wt. %, preferably from 0 wt. % to about 70 wt. %, of polymer (1).
Other monomers may be useful in preparing the step (1) compositions, including polar monomers such as hydroxyalkyl (meth)acrylates, acrylamides and substituted acrylamides, sodium styrene sulfonate and sodium vinyl sulfonate, N-vinyl-2-pyrrolidone, N-vinyl caprolactam, diallyl phthalate, dimethyl aminoethyl (meth)acrylate, and dimethylaminopropyl methacrylamide. Dimethyl acrylamide, dimethyl aminoethyl acrylamide, dimethyl aminoethyl (meth)acrylate, and dimethylaminopropyl methacrylamide are preferred. Mixtures of polar monomers also may be used. The polymerized polar monomers typically may comprise from 0 wt. % to about 30 wt. %, preferably from about 1 wt. % to about 20 wt. %, of polymer (1).
The step (1) compositions may be prepared by free radical polymerization methods well known to those skilled in the art, such as described in xe2x80x9cEmulsion Polymerization and Emulsion Polymersxe2x80x9d (Editors: P. A. Lovell and M. S. El-Aaser), J. Wiley and Sons (1997).
The step (2) compositions and their preparation are described in the prior art. Such step (2) compositions incorporate well-known commercial polymers such as natural rubber, conjugated-diene-containing polymers including butadiene-containing copolymers with acrylonitrile and/or styrene such as nitrile rubbers and SBR rubbers, polychlorobutadiene (Neoprene), hydrogenated styrene-butadiene triblock copolymers (such as Kraton(trademark) copolymers from Shell Chemical), chlorosulfonated polyethylene (such as Hypalon(trademark) polymers from E.I. duPont), ethylene copolymers (such as EPDM copolymers), acrylic and/or methacrylic ester copolymers such as Hycar(copyright) acrylic copolymers from BFGoodrich), vinyl chloride copolymers, vinylidene copolymers, polyisobutylenes, polyurethanes, polyureas, and poly(urethane-urea)s. Among preferred step (2) compositions are those comprising conjugated-diene-containing polymers, such as butadiene-containing copolymers with acrylonitrile and/or styrene (e.g., nitrile rubbers), as well as polychlorobutadienes.
Suitable step (2) compositions include those described in the following U.S. Patents, all of which are incorporated herein by reference.
For example, U.S. Pat. No. 4,920,176 relates to emulsion polymerization in order to prepare nitrile rubber (NBR) latexes. Generally, nitrile latexes comprise polymerized units of butadiene, acrylonitrile, and acrylic acid or methacrylic acid. Additional comonomers can be included to change or improve polymer properties. These include vinylpyridine, acrylic and methacrylic ester monomers, chlorobutadiene, cross-linking agents, styrenic monomers, and the like.
A review article by D. P. Tate and T. W. Bethea, Encyclopedia of Polymer Science and Engineering, Vol. 2, p.537, further describes polymers and copolymers of conjugated dienes such as butadiene rubber (BR), acrylate-butadiene rubber (ABR), chloroprene rubber (CR), isoprene rubber (IR), and styrene-butadiene rubber (SBR).
U.S. Pat. Nos. 4,292,420 and 6,020,438 relate to emulsion polymerization in order to prepare vinyl chloride latexes. Rigid polyvinylchloride can be softened by the use of plasticizers, such as 2-ethylhexyl phthalate, or by copolymerizing vinyl chloride with xe2x80x9csoftxe2x80x9dmonomers (the so-called internal plasticization monomers), which render soft copolymers with vinyl chloride. Such xe2x80x9csoftxe2x80x9d monomers include long-chain acrylic and methacrylic esters, vinyl esters, vinyl ethers, acrylamides, and methacrylamides, and are exemplified by butyl acrylate, 2-ethylhexyl methacrylate, vinyl propionate, n-octylacrylamide and the like.
U.S. Pat. No. 6,017,997 relates to preparation of waterborne polyurethane, polyurea, and poly(urethane-urea) dispersions (xe2x80x9cPUDxe2x80x9d).
Generally PUD comprises polymerized units of diisocyanate and hydrophylic moiety, together with diol, diamine, or both diol and diamine. However, all four units can have pre-polymerization functionality (i.e., number of reactive groups) higher than two. Diisocyanates can be aliphatic, such as 1,6-hexamethylene diisocyanate, cyclohexane-1,4 (or -1,3)-diisocyanate, isophorone diisocyanate, bis-(4-isocyanatocyclohexyl)-methane, 1,3- and 1,4-bis(isocyanatomethyl)cyclohexane bis-(4-isocyanato-3-methyl-cyclohexyl)-methane, tetramethyl xylylene diisocyanate, and the like.
Diisocyanates can also be aromatic, such as 2,4-diisocyanato toluene, 2,6-diisocyanato toluene, 4,4-diisocyanato diphenyl methane, and the like.
The following exemplary diols (or polyols) can be used in preparing the aforesaid PUD:
(1) Polyesters of (a) dibasic carboxylic acids, such as succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, and the like, and (b) dihydric alcohols, which include ethylene glycol, propylene glycol, butylene glycol, 1,6-hexanediol, neopentyl glycol, 1,4-bis-hydroxymethylcyclohexane, 2-methyl-1,3-propanediol; 2,2,4-trimethyl-1,3-pentanediol, polypropylene glycol, dibutylene glycol, and the like.
(2) Polycarbonate polyols containing hydroxyl groups, including those obtained from the reaction of diols, such as 1,3-propanediol, 1,4-butanediol and/or 1,6-hexanediol, diethylene glycol, triethylene glycol or tetraethylene glycol with diarylcarbonates or phosgene.
(3) Polyether polyols including polymers of alkylene oxides, such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran, epichlorohydrin, and the like.
(4) Polyacetal polyols prepared by reacting aldehydes, such as formaldehyde with glycols, such as diethylene glycol, triethylene glycol, ethoxylated 4,4xe2x80x2-dihydroxy-diphenyldimethylmethane, 1,6-hexanediol, and the like.
Diamines useful in preparing the aforesaid PUD include hydrazine, 1,2-diaminoethane, 1,6-diaminohexane, 2-methyl-1,5-pentanediamine, 2,2,4-trimethyl-1,6-hexanediamine, and the like.
In order to enable a PUD to make a stable dispersion in an aqueous medium, a hydrophilic moiety having anionic or potential anionic groups and, optionally, hydrophilic ethylene oxide units, is chemically incorporated into the PUD. The most preferred hydrophylic moiety is dimethylol propionic acid.
Well-known initiators are used in preparing the step (1) compositions and step (2) compositions, preferably a persulfate initiator, and most preferably sodium persulfate. Other initiators suitable for use include ammonium persulfate, potassium persulfate, peroxides, azo compounds, and known redox initiators such as tert-butyl hydroxy peroxide/sodium formaldehyde sulfoxylate. The initiator for preparing both step (1) compositions and step (2) compositions is preferably present in an amount from about 0.2 wt. % to about 2 wt. % based on the total weight of the polymer.
Well-known crosslinking and branching agents may be useful in preparing the step (1) compositions and step (2) compositions, such as multifunctional (meth)acrylates, (meth)acrylamides, and vinyl and allyl ethers. Examples include ethylene glycol dimethacrylate, 1.6-hexanedioldiacrylate, methylene bis-acrylamide, polybutadiene diacrylates, polyurethane diacrylates, trimethylolpropane trimethacrylate, pentaerythritol tetraallyl ether, allyl methacrylate, allyl acryloxypropionate, 4-acryloxybenzophenone, diallyl maleate, divinylbenzene, and the like. Mixtures of crosslinking and branching agents may also be used.
Another optional ingredient in the preparation of the step (1) compositions and step (2) compositions is a chain transfer agent. Useful agents include alcohols, mercaptans, halogenated compounds and mixtures thereof. Preferred agents are mercaptans. Where used, the chain transfer agent is present in an amount from about 0.1 wt. % to about 3 wt. %, preferably from about 0.1 wt. % to about 0.5 wt. % based on the total weight of the polymer.
Yet another optional ingredient in the preparation and processing of the step (1) compositions is one or more salts. The salts may be added at any time during polymerization, blending with step (2) compositions, compounding, curing, or post-processing of the compositions including during manufacture of articles. Suitable salts include LiCI, LiNO3, LiOH, LiCF3SO3, Li2SO4, and the like. Lithium nitrate is preferred. Salts typically may be used at a concentration from about 0.5 wt. % to about 10 wt. % based on the total weight of the polymer.
A step (1) composition is blended into a step (2) composition, or vice versa, with mild stirring. Additives such as activators, stabilizers, plasticizers, cross-linking and branching agents, curing agents, such as sulfur, colorants, pigments, colorants, neutralizing agents, waxes, slip and release agents, antimicrobial agents, surfactants, metals, antioxidants, UV stabilizers, antiozonants, and the like, can optionally be added to the separate latexes, to blends of the two latexes, or during manufacture of articles. Other additives may be used as appropriate in order to make dipped articles (especially flexible articles, such as gloves), or to impregnate, saturate, spray or coat papers, non-woven materials, textiles, wood, and a variety of other substrates. Applications include gloves; papers and non-wovens; fibrous materials such as textiles; rubber and plastic films, sheets, composites, and other articles such as walk-off mats; inks; adhesives; and other compositions and articles typically used in electronics, clean rooms, and automotive areas. Such articles made at least partially or even wholly (but appropriately compounded with additives, such as those described above) from the compositions of the present invention are inherently static dissipative and will not bloom, rub-off or extract during use. Articles, such as gloves made from the compositions of this invention and that meet ASTM examination standards for target tensile and elongation properties, will also have a surface resistivity value below 1xc3x971011 ohms/square, a static decay time of less than 1 second, or both.
The blends of the step (1) compositions and step (2) composition are particularly useful in the manufacture of articles such as gloves, by a coagulant dipping process, since they can readily coagulate on glove molds coated with salts such as calcium nitrate. This finding was unexpected, since PEG typically is used to make salt-stable latexes, i.e., latexes that do not coagulate readily. Coagulating dipping is well known to those skilled in the art of glove making and is described in the Kirk-Othmer Encyclopedia of Chemical Technology Third Edition, Vol. 20, pp. 453-454, as well as in the following examples. However, the step (1) and step (2) compositions can also be used in solvent dipping processes well known to those skilled in the art. Suitable solvents may be selected according to solubility of polymers and may include toluene, tetrahydrofuran, and N,N-dimethylformamide.
Also unexpected was the finding that the step (1) composition can be used without the step (2) composition in the coagulant dipping process, provided that the amount of at least one reactive macromer of at least one alkylene oxide having at least one functional group capable of free-radical transformation comprises less than about 10 wt. % of total polymer weight in the step (1) composition.